The present invention relates to a composition for forming a tantalum oxide film, a process for forming a tantalum oxide film, a tantalum oxide film and use thereof. More specifically, it relates to a composition for forming a tantalum oxide film suitable for use as an insulating film for semiconductor devices, such as a capacitor insulating film or a gate insulating film for use in DRAMs, a tantalum oxide film, a process for forming the same and use of a tantalum oxide film as an insulating film.
The area of a capacitor in a DRAM (Dynamic Random Access Memory) has been becoming smaller due to increases in the integration and density of a semiconductor device. When the capacity becomes smaller as the area of a capacitor decreases, the erroneous operation of a device may occur due to a software error or the like. Therefore, even when the area of the capacitor decreases, a sufficient capacity must be ensured. One of the means of solving this problem is to use an insulating film having a high dielectric constant (high dielectric film) as a capacitor insulating film. A SiO2 or Si3N4 film has been used as a capacitor insulating film and capacity has been ensured by a 3-D memory cell structure. However, due to a recent tendency to rapidly increase the integration and reduce the design rule of a DRAM, it is becoming difficult to ensure the capacity of a memory cell with prior art methods.
Tantalum oxide is characterized in that it has a dielectric constant 3 times or more higher than SiO2 and Si3N4 which have been used in capacitor insulating films and a thin film thereof having excellent step coverage can be easily deposited by CVD. Therefore, researches into tantalum oxide as the next-generation DRAM capacitor insulating film are now under way.
The method of forming a tantalum oxide insulating film by CVD is disclosed in Applied Physics 69(9), p. 1067 (2000). Various studies on tantalum materials used for CVD are reported in Electronic Materials, No. 7, p. 18 (2000).
However, tantalum oxide insulating films formed by these prior art methods contain large quantities of impurities and oxygen defect due to their raw materials and film forming methods, which causes a leak current and reduces dielectric breakdown. A tantalum alkoxide used as a raw material to form a film by CVD has problems that its hydrolyzability is high and that impurities such as carbon remain in the film in large quantities.
Further, film formation by CVD requires a bulky apparatus which is expensive itself and consumes a large amount of energy for vacuum and plasma systems, thereby boosting product costs.
It is an object of the present invention to provide a tantalum-containing composition for forming a high-quality tantalum oxide film easily and effectively, which solves the above problems, and a process for producing the composition.
It is another object of the present invention to provide a high-quality tantalum oxide film and a process for forming the same.
It is still another object of the present invention to provide use of a tantalum oxide film.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by a composition for forming a tantalum oxide film, comprising at least one tantalum-containing product selected from the group consisting of (A1) a reaction product of (a1) a tantalum alkoxide and (a2) at least one compound selected from the group consisting of an amino alcohol, compound having two or more hydroxyl groups in the molecule (excluding amino alcohols), xcex2-diketone, xcex2-ketoester, ester of xcex2-dicarboxylic acid, lactic acid, ethyl lactate and 1,5-cyclooctadiene and (A2) a hydrolyzate of the reaction product.
According to the present invention, secondly, the above objects and advantages of the present invention are attained by a process for forming a tantalum oxide film, comprising applying the above composition to the surface of a substrate and subjecting it to a heat treatment and/or an optical treatment.
Thirdly, the above objects and advantages of the present invention are attained by a tantalum oxide film formed by the above process.
Fourthly, the above objects and advantages of the present invention are attained by an insulating film for semiconductor devices, which has a tantalum oxide film formed by the above process.